Let's talk carefully. In XRD you are not measuring any crystalline size directly: you are just measuring the intensity of diffraction as a function of the angle of incidence. Afterwards, you apply a certain model (for instance Scherrer's equation) and, based on the assumptions of the model, you deduce the mean size of the coherent domains. Moreover, that value is the average of thousands or millions of crystallites (depending on the sample and the size of the beam).

On the other hand, in high-resolution TEM, if you are able to see the atomic planes, you can directly measure the crystalline size of that particular crystal. Generally speaking, that value would be different than the coherent domain size deduced from a XRD spectrum.

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https://www.researchgate.net/post/Why_is_there_a_difference_in_the_crystalline_size_of_the_nanoparticle_as_measured_from_TEM_image_and_XRD_analysis_of_the_same_sample

Ahmed M. Abu-Dief Why would you expect them to be the same or similar? Is an apple a pear?

XRD gives the coherent domains size which means the size of regions where there is cristallinity (do not include the grain boundaries)

TEM gives the grain size

A grain may contains more than one coherent domain

Let's talk carefully. In XRD you are not measuring any crystalline size directly: you are just measuring the intensity of diffraction as a function of the angle of incidence. Afterwards, you apply a certain model (for instance Scherrer's equation) and, based on the assumptions of the model, you deduce the mean size of the coherent domains. Moreover, that value is the average of thousands or millions of crystallites (depending on the sample and the size of the beam).

On the other hand, in high-resolution TEM, if you are able to see the atomic planes, you can directly measure the crystalline size of that particular crystal. Generally speaking, that value would be different than the coherent domain size deduced from a XRD spectrum.

I agree with Dr. Jose-Miguel Garcia- Martin

Regards

Dr.G.A. Khater

Dear Sirs

Thank you very much for your interest and sharing your valuable answers with me